Disc drives are data storage devices that store digital data in magnetic form on a rotating storage medium on a disc. Modem disc drives comprise one or more rigid discs that are coated with a magnetizable medium and mounted on the hub of a spindle motor for rotation at a constant high speed. Information is stored on the discs in a plurality of concentric circular tracks typically by an array of transducers (“heads”) mounted to a radial actuator or actuator arm for movement of the heads relative to the discs. Transducers are used to transfer data between a desired track and an external environment. During a write operation, sequential data is written onto the disc track and during a read operation, the head senses the data previously written onto the disc track and transfers the information to the external environment. Important to both of these operations is the accurate and efficient positioning of the head relative to the center of the desired track. Head positioning within a desired track is dependent on head-positioning servo-patterns, i.e., a pattern of data bits used to maintain optimum track spacing and sector timing. Servo-patterns can be recorded between the data sectors on each track of a disc, termed embedded servo, or on one dedicated surface of a disc within the disc drive, termed dedicated servo.
Servo-patterns are typically recorded on a target disc during the manufacturing of the disc drive, by a servo-track writer (STW) assembly. There are basically two conventional methods for recording servo-pattern onto a disc for use in a disc drive. In one method, an STW assembly is attached to a disc drive having a disc pack and read/write heads mounted in their proper positions. The mounted disc on the disc pack has not been pre-recorded with servo-pattern. The STW assembly attaches to the assembled disc drive and, using the actual drive's read/write heads, records the requisite servo-pattern directly to the mounted disc. Alternatively, and potentially more cost effectively, servo-pattern can be recorded onto a plurality of disc prior to the discs being mounted into a disc drive assembly. In this method, a multi-disc servo-track writer, having dedicated read/write heads or servo-recording heads records the servo-pattern onto each disc. One or more discs are simultaneously prepared within the dedicated apparatus, allowing for the high throughput output of servo ready discs. The prerecorded discs are then assembled into the drives.
Recent efforts within the disc drive industry have focused on developing cost effective disc drives capable of storing more data onto existing or smaller sized disc surfaces. One potential way of increasing data storage on a disc surface is to increase the recording density of the disc surface by increasing the track density (tracks per millimeter (tpmm)). Increased track density requires more closely spaced, narrow tracks, which in turn requires increased accuracy in recording servo-pattern onto the target disc surface. This increased accuracy requires that servo-track recording be accomplished within the increased tolerances, but remain cost effective.
Dedicated multi-disc servo-track writers have traditionally utilized servo-recording heads that are positioned on a target disc surfaces by pivoting and rotation in a radial path across the disc. The rotation of each head is typically accomplished by pivoting of an E-block within the writer, where the E-block rotates on ball bearings. Ball bearings, although effective for some existing devices, have limitations as to how precisely the servo-recording head can be position on a disc surface. For example, ball bearings often suffer from lobing, due to imperfections in the roundness of the ball bearings or smoothness of the races, which results in unwanted vibration in the servo-recording heads during servo-track recording. In addition, ball bearings suffer from a fair level of eccentricity, thereby adding a level of uncertainty as to the exact rotational movement and position of the servo-recording heads in relation to the axis of rotation. These imperfections in the manner in which the servo-recording heads are position result in an unacceptable level of accuracy, especially in light of the trend toward higher track density, cost effective, discs.
There has been a long felt but unrecognized need, in high density servo-track writing, for a mechanism to orient servo-recording heads in a substantially vibration-free manner, simultaneously maintaining a low eccentricity in their movements. Such a mechanism would allow for more accurate and cost effective recording of servo-patterns to disc surfaces and thereby allow for increases in disc track densities beyond present technology limitations. Against this backdrop the present invention has been developed.